Vehicle emission control systems may be configured to store fuel vapors from fuel tank refueling and diurnal engine operations in a fuel vapor canister, and then purge the stored vapors during a subsequent engine operation. The stored vapors may be routed to engine intake for combustion, further improving fuel economy.
The conditions for enabling purging of fuel vapors may be significantly limited, particularly in stop/start and/or hybrid powertrains. One approach to increase the rate of hydrocarbon release from the storage canister may include heating.
However, the inventors herein have recognized issues with such approaches. For example, some heating approaches can require significant electrical energy, and themselves create still further delays due to temperature dynamics. Further, the heating may be difficult to quickly isolate in specific locations where hydrocarbons are stored for a given set of storage and purging conditions. In one example, at least some of the above issues may be at least partly addressed by a method comprising adjusting a frequency of ultrasonic waves applied to a fuel vapor canister of a vehicle based on an operating condition.
In this way, ultrasonic waves can be used to quickly release hydrocarbons in different locations of the canister. For example, by adjusting the frequency of the ultrasonic waves, the waves can target different spatial positions within the canister for quicker release of stored hydrocarbons at different times of the same purging event. In an embodiment, the frequency may be adjusted during a single purge event so that at different times of the purge duration, different locations of the canister are targeted for assistance in releasing hydrocarbons so that a more complete purging of the canister is achieved in a reduced time, even if fresh air flow is limited due to limited engine vacuum, and even if certain locations within the canister are more heavily loaded with hydrocarbons than others locations within the canister, for example. The system may track the storage levels at the different spatial positions inside the canister so that the frequency can be adjusted taking into account the different storage levels, and how those levels change differently during the purge event.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.